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- "'Ilúvatar was the first beginning, and beyond that no wisdom of the Valar or of Eldar or of Men can go.'
'Who was Ilúvatar?' asked Eriol. 'Was he of the Gods?'
'Nay,' said Rúmil, 'that he was not, for he made them. Ilúvatar is the Lord for Always who dwells beyond the world; who made it and is not of it nor in it, but loves it.' "
- ― The Book of Lost Tales Part One, "The Music of the Ainur"
Eru Ilúvatar or the One is the single omniscient and omnipotent creator. He has been existing eternally in the Timeless Halls and possesses the Flame Imperishable in his spirit which kindles existence from nothingness.
 The Creator
Eru created the Ainur before anything else, whom He kindled with the Flame Imperishable. Each Ainu came from a part of His mind. To further their comprehension, he presented his thought in the form of music, and listened as the Ainur picked up his themes and elaborated on them, slowly learning to sing in harmony with each other. Eventually he showed them his greatest theme, and bade them sing it in harmony and develop it with newly granted powers. This was the Music of the Ainur.
Out of this great music, Eru showed them the Vision which showed vast halls of spaces and stories unfolded in the deeps of Time, and some Ainur were drawn to it. Eru said "ea" and thus Eä, the universe, was created.
 The God
The Ainur were not omniscient and there were some things beyond their comprehension; those were the creation of the Elves and Men, who are directly the Children of Ilúvatar (Eruhini) created without the delegation of the Ainur. Other things known by Eru alone are their destiny, and the End itself.
The activities of Eru on the life of Arda or Eä is not clear. Manwë was the vicegerent of Eru on Arda and it is known that he saught for his consent several times. Instances of Eru's direct intervention were:
- Sanctified the creation of the Dwarves by Aule, giving them life and sapience, and were his "adopted" Children.
- At the behest of Yavanna, He allowed the Ents into being.
- The creation of his Children, the Awakening of the Elves and Men.
- The Changing of the World something that the Valar themselves could not have done.
- Several coincidences and signs of higher providence throughout history, such as Bilbo Baggins finding the One Ring.
- The resurrection of Gandalf after he was killed by Durin's Bane, something that could be done by an Authority higher than the Valar.
According to Athrabeth Finrod ah Andreth Eru would someday enter Eä to save his Children. It is said that after the end of days, Eru will unite the Ainur and the Children of Ilúvatar to create a music even greater than the one of creation.
 Worship of Eru
Eru was considered trascendental, removed and distant from the affairs of Arda and was seldomly worshipped and His name was too holy to be invoked.
Feanor swore his Oath in the name of Eru. Elendil bound the Last Alliance of Elves and Men with an oath to Eru; the next known instance when a Man invoked Eru's name "who is above all thrones for ever", was by Cirion, millennia later.
 Other versions of the Legendarium
Ilúvatar appears since the earliest form of the Legendarium, in The Book of Lost Tales. It is to be noted that in earlier works of the legendarium the name Ilúvatar meant "Sky-father" since the element il- refers also to the sky (cf. Ilmen), but this etymology was dropped in favour of the newer meaning in later revisions.
Tolkien understood Eru not as a "fictional deity" but as a name in a fictional language for the actual monotheistic God, although in a mythological or fictional context. In a draft of a letter of 1954 to Peter Hastings, manager of the Newman Bookshop (a Catholic bookshop in Oxford), Tolkien defended non-orthodox aspects as rightly within the scope of his mythology, as an exploration of the infinite "potential variety" of God. Regarding the possibility of reincarnation of Elves, Hastings had written:
- "God has not used that device in any of the creations of which we have knowledge, and it seems to me to be stepping beyond the position of a sub-creator to produce it as an actual working thing, because a sub-creator, when dealing with the relations between creator and created, should use those channels which he knows the creator to have used already"
- ― Peter Hastings
Tolkien's reply contains an explanation of his view of the relation of (divine) Creation to (human) sub-creation:
- "We differ entirely about the nature of the relation of sub-creation to Creation. I should have said that liberation "from the channels the creator is known to have used already" is the fundamental function of "sub-creation", a tribute to the infinity of His potential variety [...] I am not a metaphysician; but I should have thought it a curious metaphysic — there is not one but many, indeed potentially innumerable ones — that declared the channels known (in such a finite corner as we have any inkling of) to have been used, are the only possible ones, or efficacious, or possibly acceptable to and by Him!"
- ― J.R.R. Tolkien, Letter 153
Tolkien replied to this:
- As for Tom Bombadil, I really do think you are being too serious, besides missing the point. [...] You rather remind me of a Protestant relation who to me objected to the (modern) Catholic habit of calling priests Father, because the name father belonged only to the First Person.
- God and Ilúvatar: Tolkien's Use of Biblical Parallels and Tropes in His Cosmogony by Kevin R. Hensler
- Is Eru a Good God? by Andreas Moehn (a maltheistic view)
- ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), The Silmarillion, "Ainulindalë: The Music of the Ainur"
- ↑ 2.0 2.1 J.R.R. Tolkien, Christopher Tolkien (ed.), The Silmarillion, "Quenta Silmarillion: Of the Beginning of Days"
- ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), The Silmarillion, "Quenta Silmarillion: Of Aulë and Yavanna"
- ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), The Silmarillion, "Akallabêth: The Downfall of Númenor"
- ↑ J.R.R. Tolkien, The Lord of the Rings, The Fellowship of the Ring, "The Shadow of the Past", Gandalf: "Behind that there was something else at work, beyond any design of [Sauron]. [...] Bilbo was meant to find the Ring, and not by [Sauron]. In which case you also were meant to have it. And that may be an encouraging thought"
- ↑ J.R.R. Tolkien; Humphrey Carpenter, Christopher Tolkien (eds.), The Letters of J.R.R. Tolkien, Letter 156, (dated 4 November 1954)
- ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), Morgoth's Ring, "Part Four. Athrabeth Finrod ah Andreth: 'The Debate of Finrod and Andreth'"
- ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), The Silmarillion, "Quenta Silmarillion: Of the Darkening of Valinor"
- ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), Unfinished Tales, "A Description of the Island of Númenor"
- ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), The Silmarillion, "Quenta Silmarillion: Of the Flight of the Noldor"
- ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), Unfinished Tales, "Cirion and Eorl and the Friendship of Gondor and Rohan"
- ↑ J.R.R. Tolkien, "Qenya Noun Structure", in Parma Eldalamberon XXI (edited by Christopher Gilson, Patrick H. Wynne and Arden R. Smith), p. 83
- ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), The Book of Lost Tales Part One, Appendix: Names in the Lost Tales – Part One
- ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), Morgoth's Ring